1. Field of the Invention
The present invention relates to a three-lens-group zoom lens system for a compact camera, and in particular relates to making the angle-of-view at the short focal length extremity larger.
2. Description of the Prior Art
A zoom lens system of a compact camera does not require a long back focal distance unlike a zoom lens system of a single lens reflex camera in which a space for a quick-return mirror is required behind the photographing lens system. Accordingly, a compact camera has employed a telephoto lens system including a positive powered (herein after, positive) lens group and a negative powered (hereinafter, negative) lens group, in this order from the object. On the other hand, a single lens reflex camera has employed a retrofocus lens system including a negative lens group and a positive lens group, in this order from the object.
In a conventional telephoto zoom lens system of a compact camera, the half angle-of-view at the short focal length extremity is at most about 30xc2x0. Moreover, a three-lens-group zoom lens system which can attain the half angle-of-view of more than 35xc2x0 at the short focal length extremity has not been known.
An object of the present invention is to provide a miniaturized three-lens-group zoom lens system for a compact camera in which the half angle-of-view of more than 35xc2x0 at the short focal length extremity can be attained.
In order to achieve the above-mentioned object, there is provided a zoom lens system including a negative first lens group, a positive second lens group, and a negative third lens group, in this order from the object. Zooming is performed by moving the first through third lens groups in the optical axis direction. The negative first lens group is constituted by a negative single lens element having a concave surface facing toward the object, and satisfies the following condition:
xe2x88x921 less than r1/fW less than xe2x88x920.3xe2x80x83xe2x80x83(1)
wherein
r1 designates the radius of curvature of the object-side concave surface of said negative single lens element; and
fW designates the focal length of the entire zoom lens system at the short focal length extremity.
The negative single lens element having the concave surface facing toward the object can be constituted by a negative meniscus lens element.
The zoom lens system of the present invention preferably satisfies the following condition:
50 less than xcexddxe2x80x83xe2x80x83(2)
wherein
xcexdd designates the Abbe number of the negative single lens element.
The zoom lens system of the present invention can satisfy the following condition:
1.7 less than ndxe2x80x83xe2x80x83(3)
wherein
nd designates the refractive index of the d-line of the negative single lens element.
The zoom lens system of the present invention preferably satisfies the following condition:
xe2x88x925 less than fT/f1G less than xe2x88x923xe2x80x83xe2x80x83(4)
wherein
fT designates the focal length of the entire zoom lens system at the long focal length extremity; and
f1G designates the focal length of the negative single lens element.
The zoom lens system of the present invention preferably satisfies the following condition:
0.05 less than (d12Wxe2x88x92d12T)/fW less than 0.15xe2x80x83xe2x80x83(5)
wherein
d12W designates the distance between the negative single lens element and the second lens group at the short focal length extremity; and
d12T designates the distance between the negative single lens element and the second lens group at the long focal length extremity.
The zoom lens system of the present invention can satisfy the following condition:
0.6 less than y/fw less than 0.9xe2x80x83xe2x80x83(6)
wherein
y designates the diagonal image height on a film surface.
The zoom lens system of the present invention can satisfy the following condition:
3.5 less than fT/fWxe2x80x83xe2x80x83(7)
wherein
fT designates the focal length of the entire zoom lens system at the long focal length extremity; and
fW designates the focal length of the entire zoom lens system at the short focal length extremity.
The positive second lens group includes a lens element having at least one aspherical surface, and can satisfy the following condition:
xe2x88x9230 less than xcex94IASP less than xe2x88x9210xe2x80x83xe2x80x83(8)
wherein
xcex94IASP designates the amount of change of the spherical aberration coefficient due to the aspherical surface under the condition that the focal length at the short focal length extremity is converted to 1.0.
The negative third lens group includes a lens element having at least one aspherical surface, and can satisfy the following condition:
0 less than xcex94VASP less than 0.4xe2x80x83xe2x80x83(9)
wherein
xcex94VASP designates the amount of change of the distortion coefficient due to the aspherical surface under the condition that the focal length at the short focal length extremity is converted to 1.0.
The present disclosure relates to subject matter contained in Japanese Patent Application No.2001-015740 (filed on Jan. 24, 2001) which is expressly incorporated herein in its entirety.